1. Field of the Invention
The present invention relates to a process and apparatus for extruding mixtures of thermoplastic and thermoset polymers and to articles made therefrom. More particularly, the present invention relates to a process and apparatus for extruding mixtures of thermoplastic and thermoset polymers and to articles made therefrom, wherein at least one of the polymers is recycled. Still more particularly, the present invention relates to a process and apparatus for extruding mixtures of polyolefins and recycled rubber and to articles made therefrom. Still yet more particularly, the present invention relates to a process and apparatus for extruding mixtures of polyethylene and tire particles and to articles made therefrom.
2. Description of the Related Art
Plastic materials are finding utility in more and more applications everyday. For example, plastics are used in all sorts of disposable applications such as diapers, product packaging, utensils, plates, cups, syringes, drink containers and shrink wrap. As another example, plastics are used as a major material of construction for electronic products such as telephones, computers, radios, stereos, kitchen appliances. As further example, plastics are utilized in automobiles in such applications as body molding, bumper guards, hoses, light covers, interior paneling, mud guards, floor mats and tires. In the construction industry, plastics are utilized in electrical wire, telephone wire, as paneling, horizontal surface tops, switches and moldings. Other examples, include the use of plastics in articles of clothing.
Unfortunately, as plastic materials proliferate into every facet of life, such materials become a larger portion of the waste stream. Disposable plastic items are used then disposed. Goods comprising plastic are trashed once the end of the useful life of the good is reached. Plastic waste is even generated during the process of making plastic articles in the form of off-spec material or "flash". Off-spec material may be rejected because of appearance or physical property deficiency. "Flash" refers to excess polymer on a formed article that must be removed from the formed article. The environmental pressures of today stress recycling these waste plastic materials whenever possible.
Plastics fall into one of two categories, thermoplastics and thermosets.
Thermoplastics are polymers that will have a softening temperature and a melting temperature. Examples of thermoplastics include polyvinyl chloride, nylon, polyurethane and polyolefins. Heating a thermoplastic above its softening temperature will soften it, and heating it above its melting temperature will melt it. It is easy to see that thermoplastics can be formed into a shape, melted and reformed. Thus thermoplastics lend themselves to recycling.
Thermosets, on the other hand, do not readily lend themselves to recycling. A thermoset is a polymer that solidifies or "sets" irreversibly. Examples of thermosets include, phenolics, polyesters, rubber and synthetic rubber. Since these polymers irreversibly set, heating them does not melt them into a reformable liquid. Thermosets are thus difficult to recycle.
As old vehicle tires are generally considered to constitute an environmental eyesore, many efforts have been made to recycle tires.
U.S. Pat. No. 3,210,301, issued Oct. 5, 1965, to White discloses a rubber compounding product that is made by recycling vulcanized reclaimed rubber from tires by first removing fibers and then mechanically working the rubber in the presence of 0.1-35 parts atactic polypropylene per hundred parts rubber.
Several patents disclose the use of rubber in making a molding composition. For example, U.S. Pat. No. 3,267,187, issued Aug. 6, 1966 to Slosberg et al., discloses that rubber granules may be mixed with a thermoplastic resin and molded into sheets. Also, U.S. Pat. No. 4,320,082, issued Mar. 16, 1982 to Houle, discloses a molding composition made from rubber, nylon and a vulcanizing agent, such as sulfur or magnesium oxide. U.S. Pat. No. 4,481,335, issued Nov. 6, 1984, discloses a rubber molding composition comprising tire rubber scrap, a sulfur curable polymeric binder and a curing agent for the binder. Finally, U.S. Pat. No. 4,795,603, issued Jan. 3, 1989 to Nagayasu, discloses an injection molding composition comprising 10-30 percent rubber particles and 70-90 percent polyethylene or polypropylene waste. However, these compositions are generally for batch type molding processes rather than a continuous extrusion type process.
U.S. Pat. No. 4,028,288, issued Jun. 7, 1977, and U.S Pat. No. 4,003,408, issued Jan. 18, 1977, both to Turner, both disclose processes for reclaiming tire rubber utilizing particalized tires, but excluding the metallic content thereof. Turner '288 limites the amount of cord content to less than 10 percent. Thus neither Turner patent discloses a method for processing the whole tire.
Finally, U.S. Pat. No. 4,970,043, issued Nov. 13, 1990, discloses a method of recycling "high grade" rubber having reduced debris as compared to reground rubber obtained from many automobile tires. The high grade rubber is extruded with a thermoplastic to form a semi-stable moldable product which is then cooled to form a stable moldable product. Since this process requires "high grade" rubber, tires containing debris cannot be processed.
While many attempts have been made to reuse old tires, these attempts have not been successful in producing products in processes which reuse whole tire waste, including metal and fabric belts and tire beads, or in producing products for which a sufficient need exists to utilize all of the available tire waste.